High tenacity chromium-nickel manganese austenitic steel



A ril 22, 1969 YOSHIRO ARAKI & 9

HIGH TENACITY CHROMIUM-NICKEL MANGANESE AUSTENITIC STEEL Filed Jan. 18,1966 United States Patett O 3,440,038 HIGH TENACITY CHROMIUM-NICKELMANGANESE AUSTENITIC STEEL Yosliro Arak, Tokyo, Japan, assignor toMitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed Jan. 18, 1966,Ser. No. 521,275 Claims priority, application Japan, Feb. 6, 1965,40/6,503 Int. CI. C22c 41/02, 39/26, 39/44 U.S. Cl. 75-128 4 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to new and improvedhigh tenacity austenitic steels.

The heat-resistant steels of the prior art, to be employed for exhaustvalves of internal combuston engines, for turbine blades and for thelike are generally decient in at least one respect. Among theshortcomngs of the heat-resistant sfeels of the prior art are thefollowing: extreme lowering'of the mechanical properties at hightemperatures, especially at temperatures of about 750 C.; poorprocessability, especially machinability, forgeability and weldability;only a few of these steels are both very highly oxidation-resistant athigh temperatures and very highly corrosion-resistant to -P bO; thesteels possessing a convenient hardness have poor tenacity and lowelongation; and poor fatigue resistance at high temperatures.Furthermore, previous solutions of the foregoing shortcomings have beenhighly uneconomical. A major object of this invention is to provide ahighly economical, high tenacity austenitic steel of general utility,which is 'also heat-resistant, and which has none of the shortcomingsreferred to above.

In the description of the invention which follows and in the claims, allproportions are given by weight based on the total weight of the steeland all elements and compounds are referred to by their common chemicalabbreviation (such as Mn for manganese, Ni for nickel, Cr for chromium,NiS for nickel sulfide, etc.) rather than by their full name. Since thesteels of the present invention are alloys they will frequently hereinso be referred to.

FIGS. 1 and 2 each show an engine valve incorporating alloy of thepresent invention;

FI'GS. 3 and 4 each show a precombusticn `chamber mouth piece of adiesel engine incorporating alloy of the present invention;

'FIG. S shows a turbine rotor made of an alloy of the present invention,mounted on a shaft;

FIG. 6 shows a turbocharger bl-ade made of an alloy of the presentinvention, mounted on a shaft.

Accord-ing to the present invention, Mn is found to be desirable toelevate the stability of the austenite and simultaneously to increasethe solid solubility of other elements added. By incorporating Mn in anamount not higher than 6.4% the formation of carbide is aided and thetenacity and heat-rollabil-ity of the product are improved. Ni is foundto be desirable in an amount of 6.1%-l1.l%, as by the presence thereofjointly with Mn the favo-rable effects of the Mn are augmented and3,440,038 Patented Apr. 22, 1969 F V CC the strength at both high and low temperatures is substantially improved. Because of the presence of theNi, the amount of Mn used is less than 11.9%.

Cr forms double carbides. However, it is found desirable to incorporateonly l6.0-2'2.0% Cr, which is sufficient for the attainment of goodoxidation resistance.

W forms the M C, =M C series of carbides, where the metallic (M) portionincludes Fe.Cr.W or Fe.Cr.W.Mo or the like, when the steel is heattreated. 'It is found desirable to incorporate an amount of W of up to2.l%.

It is found that N and 'C together increase the hardness and strength ofthe steel and that the presence of Mn elevates the solid solubility ofthe N. It is found that suitable amounts of N are 0.09 to 059% and of Care '0.31 to 057%.

As Si greatly increases the acid-resistance at high temperatures, theadd-tion of a small amount thereof is found to be desirable; however,because it has the tendency to subs*antially reduce the strength of thesteel -at high temperatures and, generally, when the amount of Si isgreat, the resistance to Pb'O corrosion, which re sistance is necessaryfor a valve steel, is greatly lowered, in the alloy of this invention itis found that a suitable amount of 'S-i is low, only 0.11-1.91%, so thatthe resistance to PbO corrosion is not reduced.

B greatly improves the hardenability of the steel. In the alloy of thisinvention, it is found desirable to use more B than in common heatresistant steel; however, it is also found desi'rable that the amount ofB should not be so great as to cause excessive hardness and brittlenessupon heat treatment of the steel. Accordingly, the amount -of B founddes-ira'ble is 0.005`l-0.'22%. Good carbide formation also results.

The in'corporation of 0.01-0.12% -S is found to give good machinabilityto the alloys of this invention after the beat-treatment, and by thepresence of Mn the formation of noxious sul fides, such as CrS, FeS, Nisand the like, is prevented and innoxious Mn'S is stably produced.

Mo, with W, is found to efficiently form fine carbides; but, as it isfound to have a tendency to greatly reduce the acid-resistance of thesteel at temperatures above 800 C., less than 12% -of Mo is used.

Below 045% total of Nb and/or Ta may be used ac cording to the presentinvention because they promote the stabilization of the carbides andregulation of the crystal grains.

By the addition of a small amount of other elements according to theinvention, namely, of Ti, Al, Cu and V, the hardening of the steel maybe improved and, as Al also increases the oxidation-resistance, theaddition of less than 3% total of these elements is advantageous.

In order to best coordinate the efect of the added elements, it is foundthat the following relations should obtain: Mn+Ni=1'2.0-19.0% and Thebalance of the steel of the present invention is Fe.

By a convenient heat-treating of the alloy of this invention excellenttenacity 'and processability thereof are obtained. The beat-treatmentconstitutes heating the alloy to a 'temperature of 1020-11 C. andholding it at this elevated temperature for about one hour andthereafter cooling it, for example with water, to 700-780* C. andholding it at that temperature for 4-24 hours.

'In the drawings 1 indicates steel of this invention and 2, 2', 2, 2'",and 2'' indicate heat-resistant steels of the prior art.

'FIGURE 1 shows an engine valve joined by resistance welding to a valvebody made of an alloy of this invention 1 with a valve rod made of aprior art heat-resistant steel 2, such as SEH 3 or the like. SEH 3 isthe Japanese 3 code for a steel which is 0.35-0.45% C., 1.80-2.50% Si,no more than about 06% Mn, 10-1`3% Cr, 0.70- 1.30% Mo, no more thanabout 003% P, no more than about 0.03% S and the balance Fe.

FIG'URE 2 represents an engine valve made of an alloy of this invention,applied with a stellite padding on a valve rod end, and a valve bodyworking surface, the valve body also being made of an alloy of thisinvention.

FIGURlES 3 and 4 show a precombustion ohamber mouth piece of a diseselengine made by resistance welding a mouth piece composed of alloy ofthis invention to a base seat of low alloy steel such as S 45C, SCM 3 orthe like and by adjoining the other parts therewith.

FIGURE 5 shows a turbine rotor made of the alloy of this invention witha shaft of low alloy steel such as S 45C, SCM 3 or the li ke. FIGURE 6is a turbocharger blade obtained by fixing a blade made of the al'loy ofthis invention to a shaft of S 45C, SCM 3 or the like. The alloy of thepresent invention is useful for all types of service, such as for use asa nonmagnetie material or as a heat-resistant material. S 4-5C and SCM 3are Japanese codes for steels. S 45C is 0.50-0.60% C, 0.l5-0.40% Si,0.40-080% Mn, no more than 0.45 P, no more than 0.45 S and the balanceFe. SCM 3 is 0.33-0.3-8% C, 0.1S-0.3*5% Si, 0.'60-0.85% Mn, 0.90 to1.20% Cr, `0.15-0.35% Mo, no more than 4 SEH 4 is the Japanese code foran austenitic beat-rcsistant steel which is 0.35-0.45% C, l.50-2.50% Si,no more about 0.6% Mn, 13.0-`l5.0% Ni, 14.0-16.0% Cr, 2.0-3.0% W, nomore than 003% P, no more than about 0.03% S and the balance Fe.

In perfect austenitic steel, fissures are easily originated at hightemperatures by the production of CrS; but in the alloys of the presentinvention, even if the amount of S is increased, CrS is not produced,that is, although they are not ferrite, the alloys of this invention a'cfissure-resistant. Furthermore, the alloys of this invention contain nosigma phase, the presence of which would be detrimental. They alsopossess good mechinability due to the presence of MnS instead of CrS.

The alloys of this invention possess good processability in all respectsand the machinability thereof is so good that they are able to be turnedat the rate of 160 m./rnin. Also, their weldability is good and frictionwelding thereof is possible. Furthermore, surface-treatment thereof,such as metal plating, nitriding, cementation and the like, is easy, andthey are excellent also in their ability to be heat-rolled.

The compositions and properties of seven specific alloys according tothis invention (a to g) are set forth separately in Tables 1 and 2respectively. In Table 1, the proportions of elements are by weightpercentage of the total and the unlisted balance to make 100% is Fe.

TAB LE 1 C Si M Ni Cr W N S B TAB LE 2 Tensile st'eng th, Impact value,Oxidation PbO weight Creep rupture kg./mm. Elongation, kgm./cm. Hardnessweight increase, decrease, strength, percent, 20 C. 20 C. (Re), 20 C.gr./m 900 C./ gr./dm. /h. kgJmrnfl, 20 C 800 C 100 h. 920 C. 700C./1,000 h.

003% P, no more than about 003% S and the balance Fe.

Alloys of the present invention, heat-treated as described above, have atensile strength of about 99i4 kgJrnm. at room temperature, a tensilestrength of about 4023 kg./mm. at 800 C., an impact value of above 4kgm./cm. and an elongation of above 25%, and can be -stretched at roomtemperature.

The carbide formed by the beat-treatment, having M C as a core, is verystable; the properties thereof undergo essentially no change even if itis heated up to 750 C. for 1000 hours.

Alloys of the present invention are perhaps lower in 'hardness thanheat-resistant Valve steels of the prior art; however, the strength andhardness of the alloys of this invention decrease little at hightemperatures and they have outstanding abrasion-resistance.

Alloys of this invention undergo only a small increase of oxidatior inthe atmosphere at 800 C. as Compared With room temperature; thus, forexample, this increase is only one-half that which the austeniticheat-resistant valve steel disclosed in U.S. Patent No. 2,657,130undergoes. Also, the alloys of this invention undergo only a very smallloss by corrosion into mol-ten PbO at 1000 C.; for example, the loss isas small as one-twentieth that of SEH 4 heat-resistant steel.Furthermore, in the alloys of this invention, although theoXidation-resistance is notably elevated by the presence of Si, thelowering of corrosion-resistance to PbO caused thereby is very small.

The invention is not to be construed as limited to the particular formsdescribed herein, since these are to be regarded as illustrative ratherthan restrictive.

What I claim and desire to secure by Letters Patent is:

1. A high tenacity austenitic steel consistng essentially of 0.31 to057% C, 0.11 .to 1.9l% Si, 6.4-11.9% Mn, 6.1 to 11.1% Ni, 16.0 to 220%Cr, 0.40 to 2.l0% W, 0.09 to 059% N, 0.0051 to 022% B, 0.01 to 0.12% S,and Fe, the total of Mn and Ni being 12.0 to 19% and the total of C, Si,W, N, S and B being 1.4 to 4.2%.

2. A high tenacity austenitic steel according to claim 1, furthercontaining Mo in an amount no` greater than 12%.

3. A high tenacity austenitic steel according to claim 1, furthercontaining at least one of Nb and Ta, in a total amount no greater than0.45

4. A high tenacity austenitic steel according to claim 1, furthercontaining at least one of Ti, Al, Cu and V in a total amount no greaterthan 3%.

References Cited UNITED STATES PATENTS 2,602,738 7/1952 Jennings.2,80l,9l6 8/1957 Harris 75-128.4 3,3 06,736 2/1967 Rundell.

HYLAND BIZOT, Primary Exam'ner.

